In the electrophotography, an electrical latent image is formed on an image carrier, the latent image is subsequently developed with a toner, and a toner image is transferred on a transfer material such as paper and then fixed by means of heating, pressurization, and so on. With respect to the toner to be used, in order to form not only a conventional monochromic black image but also a full color image, the image is formed by using toners of plural colors.
The toner includes a two-component system developing agent which is used upon mixing with a carrier particle and a single-component system developing agent which is used as a magnetic toner or a non-magnetic toner. With respect to the manufacturing method of such a toner, the toner is usually manufactured by a kneading and pulverization method. This kneading and pulverization method is a method for manufacturing a desired toner particle by melt kneading a binder resin, a pigment, a mold releasing agent such as waxes, a charge controlling agent, and so on and after cooling, finely pulverizing the mixture, followed by classification. An inorganic and/or organic fine particle is added on the surface of the toner particle as manufactured by the kneading and pulverization method according to the purpose, thereby obtaining a toner.
In the case of a toner particle as manufactured by the kneading and pulverization method, it is difficult to intentionally control the shape. Also, in particular, in the case of using a material with high pulverization properties, the material is liable to be finely divided. Thus, in the two-component system developing agent, the finely divided toner stuck fast to the carrier surface, thereby accelerating charge deterioration of the developing agent; and in the single-component system developing agent, the finely divided toner was scattered or developability was lowered with a change of the toner shape, resulting in deterioration of the image quality. Also, when pulverization occurs on the interface between the binder resin and the wax, the wax was separated from the toner, thereby readily generating contamination on a developing roll, an image carrier, a carrier, etc., resulting in a possible lowering of reliability as the developing agent.
Under these circumstances, in recent years, as a method for manufacturing a toner in which the shape and surface composition of the toner particle are intentionally controlled, an emulsion polymerization coagulation method is proposed in JP-A-63-282752 and JP-A-6-250439.
The emulsion polymerization coagulation method is a method in which a resin dispersion is prepared by emulsification polymerization, whereas a coloring agent dispersion having a coloring agent dispersed in a solvent is prepared, and these are mixed to form a coagulated particle corresponding to the toner particle diameter, followed by fusion by heating to obtain a toner particle. According to this emulsion polymerization coagulation method, by selecting a heating temperature condition, it is possible to arbitrarily control the toner shape from an amorphous form to a spherical form.
According to the emulsion polymerization coagulation method, it is possible to obtain a toner by coagulating and fusing at least a dispersion of a resin fine particle and a dispersion of a coloring agent under a prescribed condition. However, the emulsion polymerization coagulation method is restricted with respect to the kind of a resin which can be synthesized. Though the emulsion polymerization coagulation method is suitable for manufacturing a styrene-acrylic copolymer, it cannot be applied to polyester resins which are known to have good fixability.
In contrast, as a method for manufacturing a toner using a polyester resin, there is an inverse emulsification method in which a pigment dispersion and the like are added in a solution dissolved in an organic solvent, to which is then added water. However, in this method, the organic solvent must be recovered. A method for manufacturing a fine particle by mechanical stirring in an aqueous medium without using an organic solvent is proposed in JP-A-9-311502. However, in this method, a resin in a molten state and the like must be fed into a stirring device, and handling was difficult. Also, a degree of freedom against the shape control was low so that it was impossible to arbitrarily control the toner shape from an amorphous form to a spherical form.